In recent years, applications of image forming apparatus such as electrophotographic copying machines, etc. have been expanding, and there has been a demand in a market for a higher level of image quality. Particularly, with respect to office documents, etc., in addition to developments of the image copying techniques or latent image-forming techniques at the time of inputting, also at the time of outputting, the types of hieroglyphic characters have become richer and more refined, and due to dissemination and development of presentation software, reproducibility of latent images of extremely high quality is desired so that there will be little defects or unsharpness in printed images. Particularly, as a developer to be used in a case where latent images on a latent image substrate constituting an image forming apparatus are line images of at most 100 μm (at least about 300 dpi), a conventional toner is usually poor in reproducibility of such fine lines, whereby sharpness of line images has not yet been sufficient.
Particularly, in the case of an image forming apparatus such as an electrophotographic printer using digital image signals, a latent image is formed by a gathering of certain prescribed dot units, and a solid portion, a half-tone portion and a light portion are expressed by changing the dot density. However, if toner matrix particles are not accurately disposed at the dot units and mismatching occurs between the positions of dot units and the actually placed toner positions, there will be a problem such that no gradation of the toner image is obtainable which corresponds to the ratio in the dot density between a black portion and a white portion of a latent image. Further, if, in order to improve the image quality, the dot size is reduced to improve the resolution, the reproducibility of a latent image to be formed of such fine dots, tends to be further difficult, and it is unavoidable that the image tends to be poor in gradation with high resolution and poor in sharpness.
Therefore, it has been proposed to regulate the particle size distribution of a developer to improve the reproducibility of fine dots thereby to improve the image quality. Patent Document 1 proposes a toner having an average particle size of from 6 to 8 μm, and it has been attempted to form a latent image of fine dots with good reproducibility by making the particle size fine. Further, Patent Document 2 discloses a toner having a weight average particle size of from 4 and 8 μm and toner matrix particles containing from 17 to 60% in number of toner matrix particles having a particle size of at most 5 μm. Further, Patent Document 3 discloses a magnetic toner containing from 17 to 60% in number of magnetic toner matrix particles having a particle size of at most 5 μm. Patent Document 4 discloses toner matrix particles wherein, in the particle size distribution of the toner, the content of the toner matrix particles having a particle size of from 2.0 to 4.0 μm is from 15 to 40% in number. Further, Patent Document 5 discloses a toner containing from about 15 to 65% in number of particles of at most 5 μm. Further, Patent Document Nos. 6 and 7 disclose similar toners. Further, Patent Document 8 is discloses a toner which contains from 17 to 60% in number of toner matrix particles having a particle size of at most 5 μm, contains from 1 to 30% in number of toner matrix particles having a particle size of from 8 to 12.7 μm and contains at most 2.0 vol % of toner matrix particles having a particle size of at least 16 μm and which has a volume average particle size of from 4 to 10 μm and has a specific particle size distribution with a toner of at most 5 μm.
However, each of these toners is one containing a large amount (i.e. % in number) of particles of at most 3.56 μm exceeding the upper limit of the right-hand side of the formula (1) of the present invention, which means that it is a toner wherein, in a relative relation between the particle size and fine powder, the proportion of fine powder remaining is relatively large as compared with a toner having a prescribed particle size. In such a toner wherein the proportion of fine powder is still large, there will be particles not sufficiently electrified by a developing method where a toner having a quick rising in electrification is required particularly in such a case where electrification is done instantaneously by friction as in a non-magnetic one component developing method, whereby there have been problems such that the toner is likely to fall off or be blown off from the developing roller, that the image density fluctuates to form ghosts by selectively picking up a print history of the first rotation of the developing roller in the second or subsequent rotation of the roller, that the drum cleaning tends to be inadequate and that soiling of printed images is likely to result due to failure to form a toner layer on the developing roller.
In recent years, enhanced life and high speed printing have been desired in addition to the demand in the market for high image quality. However, such demands also have not yet been fully satisfied by conventional toners. If a fine powder is contained in a substantial amount like in a conventional toner, there has been a problem such that the fine powder contaminates components in continuous printing, whereby the ability to charge the toner or the like tends to decrease to cause non-uniformity of the image, and when such a toner is introduced into a high speed printing machine, scattering of the toner tends to be remarkable.
Further, it has been one of important objectives to prepare an electrophotographic photoreceptor which presents good matching with a toner having a small particle size.
Patent Document 1: JP-A-2-284158
Patent Document 2: JP-A-5-119530
Patent Document 3: JP-A-1-221755
Patent Document 4: JP-A-6-289648
Patent Document 5: JP-A-2001-134005
Patent Document 6: JP-A-11-174731
Patent Document 7: JP-A-11-362389
Patent Document 8: JP-A-2-000877